1. Field of the Invention
The invention relates to a centrifugal pump.
2. Discussion of the Related Art
For sealing off the interior of a pump from the atmosphere the most various different types of seals are known. This is a result of the type of fluid pumped, its degree of hazard and its sensitivity, the resistance to wear of a slip ring seal with respect to the fluid pumped or, respectively, the pressure of pumping and the accessibility to the slip ring seal itself. A simple solution in this respect is the ETACHROM N pump as sold by the applicant, in which within the pump housing a slip ring seal is arranged directly between the impeller and the housing.
Under difficult conditions double acting slip ring seals or even tandem seals are employed. Thus the German patent publication 1,269,436 C discloses an arrangement having an outer, double acting slip ring seal in a multi-part seal housing. In this case a special carrier is utilized, which is secured to the shaft and overlaps the slip ring seal arranged on a smaller diameter. On the outer diameter of the carrier a second slip ring seal is then arranged, which bears against a point in the seal housing. The slip rings are in this case generally arranged in the same radial plane.
A slip ring seal housing is disclosed in the U.S. Pat. No. 4,900,039, within which two slip ring seals are arranged on different diameters. The sliding surfaces thereof are simultaneously in engagement with a single rotary shaft ring. This special design with a rotary shaft ring and two stationary, non-moving counter rings is to render possible further operation with the aid of the other seal if one seal should fail.
In the case of the design in accordance with the U.S. Pat. No. 2,831,712 a double slip ring seal is arranged between the high pressure side to be sealed off and the atmosphere. In the space between the two slip ring seals a specially designed valve mechanism is to be utilized to maintain a constant differential pressure. As rotary slip rings use ring seals employed.
The present invention is directed toward a slip ring seal housing for centrifugal pumps, which can be employed for a plurality of pumps.
The present invention completely dispenses with any special slip ring seal housing, since the slip ring seal simply bears against a thrust cover, which is necessary for each pump, in the axial direction. The use of at least two counter abutments for the slip ring seal support in the axial direction renders possible an extremely wide range of variation owing to the use of the thrust cover in series of pump designs. Owing to the use of standardized seals it is possible for the user of a pump to select in a simple fashion which type of slip ring seal is to be utilized in his plant. For reasons of simplification of stock holding and reduction of costs he will generally prefer a slip ring seal type, which is already being used for his pumps.
The pump can be operated without difficulties with only a single slip ring, which is arranged on the large or small diameter. If the thrust cover is used on machines with a high drive power, there is then sufficient space available adjacent to the opening for the shaft in order to introduce a drive shaft with a larger diameter into the housing. In such a case only a single slip ring seal, arranged on the larger diameter, would be employed, since there would then no longer be space for the use of a slip ring seal arranged on the smaller diameter.
In accordance with one embodiment of the invention the slip ring seals able to be mounted on the smaller diameter are directly arranged on the drive shaft in a sealing fashion. This renders possible the use of small, low-price slip ring seals and furthermore a design without any so-called shaft protection sleeve.
Again in accordance with a further development of the invention one or both slip ring seals are arranged to engage the hub of an impeller of the last pump stage with a supporting action. This may be provided for directly or indirectly with the intermediate placement of a sealing ring. For instance, the slip ring seal located on the smaller diameter would bear against the hub end of an impeller and the slip ring seal arranged thereover, located on the larger diameter, would bear against a ledge on the hub of the impeller. The thrust cover can be utilized both on a single or a multiple stage pump, in which case in the former instance the last pump stage would be identical to the single pump stage.
In those cases, in which the use of a double slip ring seal is preferred, connections will be provided in the thrust cover in the part between the counter abutments for a liquid seal. These connections may be provided as need be or they can be permanently provided, in which case it is merely necessary to remove plugs. Accordingly it is possible to supply a cooling or flushing liquid into the space between the two slip ring seals. Simultaneously there is then a possibility of checking for the sealing action. If the liquid level remains constant in a container connected with a connection for a liquid duct, the sealing action of the slip ring seals will be constant as well. On the other hand if it changes, the sealing action of the one or the other slip ring seal will be defective. Furthermore not having a complete slip ring seal housing and an arrangement in accordance with the invention will furthermore lead to unusually rapid and simple fitting of the seal.